Static mixers have long been employed to promote and to enhance the mixing of one or more fluids within a defined space. Mixers can contain active elements such as paddles and rotors, although it is quite common to provide static elements whereby the turbulent flow of fluids in and around these elements enhance fluid mixing without the need for moving parts which inherently add to the cost of mixing operation both in terms of power requirements and labor intensive maintenance procedures. Many static mixers rely on mixing element configurations which present a set of interstices to the product flow. Elements of this type divide a fluid stream along the mixing path and recombine locally created substreams into a more homogeneous mixture.
It is also common practice to provide, within a conduit, a series of tubes or pipes to effect heat transfer between a product stream and a fluid medium contained within tubes in contact with the flow of the fluid product.
The art is replete with both patented and non-patented literature describing various approaches to motionless mixer design. One of the earliest devices was developed at the Arthur D. Little Co. and licensed to others. The Arthur D. Little design employed helical mixing elements which acted to divide a passing fluid into two streams. When "n" of such elements were installed in a series, they produced a total of 2.sup.n divisions of the stream. Applicant's own static mixer, as described in U.S. Pat. No. 3,923,288, dated Dec. 2, 1975, is of this type. There have been other motionless mixer designs, all of which have been a variation on the basic theme of fluid division and recombination. For example, U.S. Pat. No. 4,511,258, dated Apr. 16, 1985, discloses a motionless mixing device having mixing elements formed by deforming flat stock material. Sulzer Brothers Ltd. was awarded U.S. Pat. No. 4,211,277 on Jul. 8, 1980, for a heat exchanger with a plurality of fittings which are disposed in the flow passage. The fittings were taught to be constructed of groups of webs with each group disposed in spaced parallel relation in an angular orientation to the axis of the flow passage. Each group of webs was disposed in crossing relation to the webs of an adjacent group to improve heat transfer with reduced pressure loss. Koch Engineering Co. was granted U.S. Pat. No. 4,643,584 on Feb. 17, 1987, for a motionless mixer for use in mixing turbulent flow streams in a conduit. The mixer of the '584 patent comprised at least first and second pairs of plate elements, the plate elements composed of semi-elliptical portions disposed at an angle of about 45.degree. from the axis of the conduit, the first and second pairs disposed at an angle of about 90.degree. with respect to each other in the conduit with the plate elements of each pair overlapping the plate elements of an adjacent pair. It was the goal of the '584 patent to provide sets of interstices to divide local flow into two streams and to divert each stream away from the other to develop a lateral or radial flow distribution.
Although the above-described prior art representing a small segment of the available teachings of motionless mixers perform the mixing function to a certain degree, none of the existing types of static mixing devices produce a uniform distribution of interstices throughout the available volume within the conduit, Applicant has now found that by providing such a uniform distribution of interstices, uniform mixing is enhanced by maximizing the volume utilization in terms of interstice mixing regions for a given pressure drop. As such, Applicant's present design provides for a more efficient mixing apparatus.